The invention relates to a device for detecting a trailer coupled onto a tractor vehicle with a switch and a relay which can be activated by this switch being provided in the tractor vehicle, by means of which switch lights of the tractor vehicle can be switched via a first line and corresponding lights of the trailer can be switched via a second line, with an input of a logic element being connected to a branching point in the second line, which branching point is located between the lights, the logic element then transmits a signal at its output when the trailer is coupled on, and with a resistance being connected between battery voltage and the branching point, which resistance is of high value compared with the resistance of the trailer lights.
A generic device is already known (German Patent Specification No. 3,038,464) which is based on the fundamental principle that the low-resistance direction-indicator lights in the trailer lower the 1-signals at a logic element to a 0-signam and therefore trigger an indication. The switching arrangement shown, however, presupposes that lights continuously applied to earth are used, which is only the case with the direction-indicator lights.
The object of the invention is to provide a generic device in such a way that it can be used in all light circuits, irrespective of whether these lights are switched on continuously in operation.
This operation is achieved according to the invention wherein a switch is also at battery voltage (U.sub.B), in the closed condition of which a switch contact of an activated relay bridges a resistance and a coil of a second switch is switched into a second line between a branching point and lights, which second switch on one side, is also connected to battery voltage (U.sub.B) and, on the other side, is connected to a second input of a logic element.
Another object of the invention is a device for detecting when a trailer is coupled onto a vehicle, with a first switch and a relay which can be activated by the first switch being provided in the vehicle, by means of which switch lights of the tractor vehicle can be switched via a first line and corresponding lights of the trailer can be switched via a second line, with an input of a logic means connected to a branching point in said second line, which branch point is located between an electrical source and said trailer lights, which logic means transmitting a signal at its output when the trailer is electrically coupled to the vehicle between a battery voltage and the branching point and is of high value compared with the resistance of the trailer lights, wherein the first switch is also at battery voltage in a closed condition and a switch contact of the relay bridges the resistance, a coil of a second switch is switched into the second line between the branching point and the trailer lights, when second switch is also connected between battery voltage and a second input of the logic element.
It is another object of the invention to provide a device for indicating electrical status of an electrical socket on a vehicle comprising switch means for connecting at least a vehicle light and a first relay to an electrical source, a branch point, a resistance means connected between said electrical source and said branch point, second switch means responsive to said first relay for connecting the branch point to said electrical source, second relay means responsive to a voltage between said branch point and said electrical socket on said vehicle to provide an output, and logic means responsive to a potential at said branch point and to said output to generate an indicating signal.
It is another object of the invention to provide a device for indicating electrical status of an electrical socket on a vehicle comprising switch means for connecting at least a vehicle light and a first relay to an electrical source, a branch point, a resistance means connected between said electrical source and said branch point, second switch means responsive to said first relay for connecting the branch point to said electrical source, second relay means responsive to a voltage between said branch point and said electrical socket on said vehicle to provide an output, and logic means responsive to a potential at said branch point and to said output to generate an indicating signal wherein an electrical socket on a trailer is connected to said electrical socket on said vehicle and further comprising at least a trailer light connected to said electrical socket on said trailer and responsive to said first switch means.
The foregoing and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for the purposes of illustration only, one embodiment in accordance with the present invention, and wherein like reference numerals are used to designate like parts.